VisualGPS is a program that offers users the opportunity to monitor live operation of a GPS connected to a PC serial port. It features a dashboard style instrument cluster that displays dynamic changes in direction, speed, and altitude. A bar graph style satellite acquisition and signal strength window and an azimuth sky view satellite location and triangulation chart give you a real-time visual view of GPS activity. The Command Window displays the raw data stream exiting the GPS serial connector. A short drive around town with the DigiTraveler GPS sitting on the dash connected to a notebook computer running VisualGPS made all I have learned about GPS come to life on the screen. Its much more informative than using mapping software that simply positions your location on a map.
Below is an actual screen shot of the VisualGPS Command Window. The GPS continuously spits out NMEA data sentences in real-time. This is done at a rate of one sentence per second. Each repetition of sentences provides new updated information approximately every six seconds.
The sentence of most importance to us is the one starting with $GPRMC. Look at the fifth sentence from the top of the window: $GPRMC,020922,A,4307.5239,N,07742.8355,W,008.7,281.8,181203,,*09
Interpreted as follows:
 | RMC Recommended Minimum sentenCe |
| 020922 Fix taken at 02:09:22 UTC |
| A Status A=active (the data status. [A] for valid data, [V] for invalid) |
| 4307.5239,N Latitude 43 deg 07.5239' N |
| 07742.8355,W Longitude 77 deg 42.8355' W |
| 008.7 Speed over the ground in knots |
| 281.8 Track angle in degrees True |
| 181203 Date - 18th of December 2003 |
| *09 The checksum data, always begins with * |
